1. Field of the Invention
The present invention relates to a gas turbine stationary blade which enables cooling without a pressure drop of the cooling vapor by the use of a simple structure.
2. Description of the Prior Art
As a recent tendency of industrial gas turbine, a turbine inlet gas temperature is gradually increased to obtain a high output and high efficiency. The temperature is now anticipated to reach as high as 1,500.degree. C. Therefore, a gas turbine stationary blade is sometimes cooled by the use of vapor (steam), having a high cooling effect, which flows within the blade. One example of a prior art cooling structure for a gas turbine stationary blade by way of vapor cooling is shown in FIGS. 3 and 4. The cooling vapor, supplied from a cooling vapor inlet 5 of an outer shroud 3, (as shown by arrows) passes through an impingement plate 13 having a multitude of fine holes and then passes through an inward cooling passage 7 within a blade unit 2 to cool a blade face. Then, it enters a finned internal cooling passage 9 (provided within an inner shroud 4a) to cool the inner shroud 4a. Next, the cooling vapor passes through an outward cooling passage 8 within the blade unit 2 to be discharged outside of a cooling vapor outlet 6 of the outer shroud 3 and to be collected in its entire amount.
In the prior art gas turbine stationary blade employing vapor cooling (as shown in FIGS. 3 and 4), the inner shroud 4a, through which the cooling vapor flows from the inward cooling passage 7 within the blade unit 2 to the outward cooling passage 8, has a complicated cooling passage configuration. There is a difficulty in the art of manufacture thereof, which leads to a problem of high cost. Also, there is a problem of a large pressure drop of the cooling vapor when it passes through a narrow portion of the inner shroud 4a, which leads to lowering of gas turbine efficiency.